1. Field of the Invention
The present invention relates to a capacitor embedded printed circuit board (PCB), and more particularly, to a capacitor embedded PCB, capable of decreasing an inductance by controlling an electrode structure of the embedded capacitor and of easily embodying high capacitance for unit area by controlling a number of multilayers and an area of electrodes.
2. Description of the Related Art
In general, a capacitor is a device storing energy as the form of charges and has properties, in which charges are stored and a current does not flows in the case of a direct current (DC) power source and a current flows in proportion to a change in voltage according to a capacitance of the capacitor and time while the capacitor is charged/discharged in the case of an alternating current (AC).
Due to such properties, capacitors are essential passive devices used for coupling and decoupling, filtering, impedance matching, charge pumping, and demodulation in such as digital circuits, analog circuits, and electric electronic circuits such as high frequency circuits and generally manufactured in various forms such as chips and disks and mounted on a surface on a PCB to be used.
However, as electronic devices become miniaturized and complicated, an area for mounting passive elements on a PCB is reduced. Also, as speed of electronic devices becomes high, frequency is increased. Thereupon, parasitic impedances occurring due to various causes such as a conductor or solder between passive devices and an integrated chip (IC) cause various problems. To solve problems, various attempts to embed a capacitor in a PCB are made.
Up to now, on a surface of general PCBs, a general discrete chip resistor or a general discrete chip capacitor is mounted. However, recently, PCBs with a passive device such as a resistor or capacitor, embedded therein, have been developed.
Passive device embedded PCB technology indicates that a passive device such as a resistor or capacitor is inserted into an inner layer of a board by using new materials and processes and replaces a conventional chip resistor or chip capacitor. That is, a PCB with a passive device embedded therein has the passive device, for example, a capacitor embedded in an inner layer or the outside of the board itself. Regardless of a size of the board, when the capacitor that is a passive device is integrated into the PCB as a part, the capacitor is called as an “embedded capacitor” and the PCB is called as an “capacitor embedded PCB”. Most important feature of the capacitor embedded PCB is that there is no need to mount a capacitor on a surface of a PCB since the capacitor is provided as a part of the PCB.
To manufacture a wireless terminal miniaturized while having various functions, it is required to use a higher RF bandwidth. According to this, self resonance frequency of a passive device is required to be higher. Also, in the case of a decoupling capacitor used for power source stabilization, it is required to reduce impedance at high frequency.
FIG. 1 is a cross-sectional view illustrating a conventional capacitor embedded PCB.
Referring to FIG. 1, a capacitor includes inner electrodes 14 and 17 and a dielectric layer 11 interposed between the inner electrodes 14 and 17. The inner electrodes 14 and 17 are connected to positive and negative electrodes via via holes 16 and 19, respectively. In the capacitor embedded PCB, directions of currents passing through an anode and cathode of the capacitor embedded in the PCB are allowed to be opposite to each other to compensate parasitic inductance occurring due to the current, thereby reducing entire parasitic inductance.
However, in the case of PCB where a conventional capacitor is embedded, it is advantageous to reduce inductance but a capacitance value thereof is too small to be actually used.